Field of the Invention
The present invention relates to a multiple variable valve lift apparatus. More particularly, the present invention relates to a multiple variable valve lift apparatus to realize multiple valve lifts which includes zero lift.
Description of Related Art
Generally, an internal combustion engine receives fuel and air into a combustion chamber and generates power by combusting the fuel and the air. Herein, an intake valve is operated by drive of a camshaft, and air flows into the combustion chamber during when the intake valve is open. In addition, an exhaust valve is operated by drive of a camshaft, and air is exhausted from the combustion chamber while the exhaust valve is open.
Meanwhile, optimal operations of the intake valve or the exhaust valve are determined according to rotation speed of the engine. That is, lift and open/close timing of the valves are properly controlled according to rotation speed of the engine. A variable valve lift (VVL) apparatus has been developed in which the valves are operated for various lifts according to rotation speed of the engine for realizing optimal operations of the valves according to rotation speed of the engine. For example, there is a cam shift type variable valve lift apparatus in which a plurality of cams for operating the valves by each different lift are provided to the camshaft, and the cam operating the valves is selected according to conditions.
If a journal disposed between a cam and another cam is formed to be lengthy along axial direction for cam shift in a variable valve lift apparatus which is configured so that cams are arranged in parallel with each other for operating two valves, it is not easy that the variable valve lift apparatus is applied to a small engine having a narrow gap between two valves.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.